Transmission circuits



, J. F. FARRINGTON TRANSMISSION CIRCUITS Filed July 31, 1923 mvenror Jab/7 f/Zrrnhy/on Patented Jan. 3, 1928.

UNITED STATES JOHN-F. FARBINGTON, or FLUSI-IING, NEW YORK, AsSIGN R r0 WESTERN ELECTRIC COMPANY, INCORPORATED, on NEW YORK, N. Y., A CORPORATION on NEW YORK.

'rRANs vrI'ssIoN cmcur'rs.

A ncauoa filed July 31,

The invention relates to transmitting'cir-J cuitsand particularly to a transmittingsys' tem employing a change-over switch which in one position connects the transmitting conductor to the transmitting and receiving circuits forsimultaneous transmission and.

In operating a circuit of this character, es-

' pecially where the transmitting conductor is a radio antenna as in the preferred form of the invention, it has been found thatwhen the anode circuits of the vacuum tubes in the transmitting circuit are made or broken to change from receiving to transmitting, or vice versa, or to change from simplex to duplex operation, or vice versa, surges of current are caused in the vacuum tube circuits of sufficient intensity to trip the circuit break-er or blow the fuses in the direct current power supply, or in some cases the tubes themselves are rendered temporarily or permanently in0perative.

An object of the invention is to prevent surges of current in the tube circuits in order that the transmitting circuit may be maintained in an operative condition. This is accomplished bypermanently connecting in circuit a sufiicient number of the vacuum tube devices, so that the surges due to switching on and ofi the remaining tubes, are not objectionably large.

With a circuit of the above mentioned type it has been proposed to use, when the circuit is connected for duplex operation, a trap or anti-resonant circuit, tuned tothe transmitted frequency, in order to keep currents of this frequencyout of the local receiving circuit, which also includes a tuned circuit. It has been found in adjusting the circuit that, if the trap is out of tune,'in tuning the receiving circuit a. condition may be reached where thereactance of the tra is neutralized by the reactance of the receiving circuit. This results in abnormally large potentials being applied to the receiving circuit.

Another object of the invention is to protectthe receiving circuit against such ab- 1923. Serial No. 654,824.

normal potentialsf This is accomplished by preventing the abnormal potentials from reaching the receivingcircuit, for instance, by connecting a protective gap across the receiving I circuit. Preferably this gap comprises closely adjacent stationaryzcontact points of the change-over switch, in order that this switch when in a position for simplex operation will short circuit the receivmg circuit. Circuit connections are also provided whereby the switching operation just pientioned also serves to short circuit the rap. For further details of the invention, reference may be made to the drawings wherein a radio signaling circuit adapted for simplex and duplex operation is schematically represented; 1

, Referring in detail to the drawings, the voice amplifier V, the modulatortube M, the oscillator tube 0, andthe high frequency amplifier HA, are electron discharge devices connected substantially as shown in British Patent N0. 168,056; to supply modulated high frequency oscillations. ,4

The alternating current: power. supply for all of the filaments which are connected in parallel is that'of'U. S. Patent No. 1,432,022. and will not be described in detailhere.

The generator 1 which is provided with a.

suitable low pass filter 2 supplies direct cur rent to the anode circuits of all of the tubes.

It is to be noted thatthe anodecircuit of tube V is permanently connected to the generator 1; at least'its anode circuit isindependent of the transmit-receive relay 3, whereas, the anode circuits for p the other three-tubes arecompleted through contacts 4 and 5 of this relay. The reason for this has been explained above and is to prevent surges from rendering the circuitinoperative when the'generator 1 is connectedto the plates or anodes of the tubes Preferably a condenser 30, connected in shunt to contacts 4e and 5, is. employed to prevent sparking at these contacts. I I i v The'inductances 6;? and 8 in the anode circuits of tubes M, O, and HA, respectively. prevent parasitic oscillations, as described and claimed in the.U. S..patent to. Schelleng, N0. Mercer-November 28,1922- In order to. prevent high frequency. currents in the output.circuitofithetuhe HA from being supplied to the previous tubes in the series, the high frequency filter comprising the inductance 9 and condenser 10, is employed. As shown, this lilter'comprises only a single section, the series element being the high frequency choke coil 9, and the shunt element being thecondenser 10 which passes the high frequency currents readily. Obviously, a iilter comprising a plurality of sections could'be used inplace of the single section filter shown. v

The coil 11 in the outputcircuit of tube HA serves to transmit to the antenna the modulated high frequency waves, the connection of this coil in the antenna circuit being as follows: ground 12, tuning inductance 13, condenser 1-fl, coil 11, condenser 10, ground 12. The current in section 13 of the tuning inductance induces a potential difference between the ground 12 and the antenna 15 through the transformer action of the tuning inductance 13. The antenna circuit includes, if desired, a variometer and condenser 17. i

The receiving apparatus which may be of any desired type is shown as inductively coupled to a circuit 18, grounded at 19 and tuned to the desired frequency.

For simplex or push-button operation, the -double-pole double-throw switch S is thrown to the right. The circuit is then in condition to be changed from trans nit to receive in accordance with the operation of the push button 20. Whenthis. push button is operated, relay 3 is energized or deenergized over an obvious circuit. l vith relay 3 in the position shown, the transmitting circuit is connected through contacts 21 and of relay 3 tothe antenna 15, and thereceiving circuit is'short-circuited between ground 12 and ground 19 over an obvious circuit which includes the contacts 23 and-24L of relay 8, the stationary contacts 25 and 26 and blade 27 of switch S. The trap circuit T is tuned to the high frequency to be transmitted, but with switch S to the right as just assumed, this trap circuit is short-circuited through contacts 25 and 26, and blade 27 of switch S. With relay 3 deenergized the receiving circuit R, is connected. to the antenna over an obvious circuit, the transmitting circuit then being disconnected.

Nith the switch S thrown to the lei't, the circuit is adapted for duplex operation, the antenna now being connected both to the transmitting circuit, as previously traced, as well as to the receiving circuit through blade 27, trap 'l, and contacts 23and 24 to circuit 18. The blade 28 of switch S now energizes relay through the grounded stationary contact 29 independently of the pushbutton 20. l v

' A protective'gap, as above described, is provided for thereceiving circuit by the spaced switch contacts 25 and 26, contact 25 being connected to the ungrounded side of leaving .the anode circuit of one of said tubes energized, and in reducing the energization of the anode circuit of another tube when said transmitting circuit is inopera tively related to the outgoing line. Y

2. A transmitting circuit comprising a plurality of vacuum tube devices, a source of potential for the anodes of said devices, and a change-over switch for disconnecting one of said devices from said source for rendering said transmitting circuit ineiiective while leaving another of said devices connected thereto.

A combined sending and receivingcircuit comprising a trap circuit tuned to the sending frequency, a protective gap in shunt to the receiving circuit, and switching means consisting of cont-acts and a movable arm for bridging said gap and short-circuiting said trap circuit. 1

4;. A simplex-duplex sending and receiving circuit comprising a trap circuit tuned to the sending frequency and effective for duplex operation, and switching means for rendering said trap circuit and said receiving circuit ineilective when transmitting simplex.

5. In a simplex-duplex transmitting and receiving system, means for preventing ab normal surges in the transmitting circuit when the transmitter is. deenergi'ze-d and means for preventing abnormal surges in the receiving circuit when the transmitter is energized.

6. In a transmitting system containing vacuum tubes, means for rendering said sys tem inoperative for transmission, and means for removing the anode potential from certain oil? said tubes when the transn' itter is inoperative while leaving the potential applied to other 0t said tubes.

7. In a simplex-duplex transmitting and receiving system, means for preventing ab- 1 normal surges in the transn'iitting circuit when the transn'iitter is rendered inoperative in simplex operation and means for preventing abnormal surges in the receiving circuit in duplex operation.

'8. In a simplex-duplextransmitting and receiving system, switching means toada'pt the circuit to duplex or simplex operation, means. for preventing abnormal surges in the transmitting circuit when the transinitter is rendered inoperative in thesimplex operation, and means for preventing abnormal surges in the receiving circuit in duplex operation.

9. In a simplex-duplex transmitting and receiving circuit containing vacuum tubes, means for removing the anode potential from certain of said tubes while leaving the potential applied to other of said tubes when the transmitter is rendered inoperative in simplex operation and means comprising a trap circuit to prevent abnormal surges in the receiving circuit in duplex operation.

10. In a simplex duplex transmitting and receiving system containing space discharge;

devices. means for removing the anode potential from certain of said tubes while leav-g apparatus in duplex operation, and a switch to short circuit said gap in simplex operation.

12. In a simplex-duplex transmitting and receiving system containing space discharge tubes, a switch for changing from simplex to duplex operation, an antenna change-over switch for simplex operation, a trap and safety gap short circuited by said first mensurges in a transmitting system when the transmitter is rendered inoperative which comprises removing the potential from the anodes of certain of said tubes while leaving receiving system including vacuum tubes which consists of removing the potential.

from the anodes of certain 01 said tubes 'while'leaving the potential applied to anodes of other of said tubes when the transmitter is rendered inoperative in simplex operation and inserting a protective device to protect the receiver from abnormal surges in duplex operation.

In witness whereof, I hereunto subscribe my name this 24th day of July A. D.,1923.

- JOHN F. FARRINGTON. 

